Why Film Cannot Run on a Rigid-Plastic Line

LDPE film, agricultural film, shopping bags, woven bags, jumbo bags and mixed flexible packaging all share one property that breaks rigid-plastic equipment: very low bulk density combined with a tendency to entangle. Three things go wrong when you feed film into a line designed for bottles and crates.

• It wraps. Film climbs rotating shafts and rotor ends instead of being drawn into the cutting chamber, so the machine stalls while the belt keeps running.
• It floats. In a float-sink tank the fraction you want to wash is the fraction that will not sink, so density separation stops doing its job.
• It carries water. A centrifugal dewaterer that works well on PET flake cannot throw water out of a continuous film sheet; the water stays trapped between layers.

The consequence is a design principle rather than a component choice. A film and flexible plastic washing line is built around gentle conveying, wet size reduction, intensive washing and squeezing — the opposite of the crushing-first logic used for rigid scrap, where a crusher can be fed freely and flake sinks for separation.

The Six Stages of a Film Washing Line

The published process sequence for LVKESORT film lines has six stages, and the first two are the ones that decide whether the rest of the plant runs at all:

Read the list again and notice where the size reduction sits: stage three, after the film has already been metered and de-tangled, and performed in water rather than in dry air. That single decision does two jobs at once. Cutting in water keeps the film moving through the cutting zone, and the water bath starts removing soil from the freshly cut edges at the same moment. On a dry rigid-plastic crusher the same operation would instead leave a mat of film around the rotor.

Reference Line Configurations

The published WL series covers four reference configurations. The table below is the series data as published on the product page:

One reading note matters more for film than for any other material. Film lines are sized by wet throughput, and wet throughput is lower than the dry figure for the same model. Bulk density and contamination level drive that gap: a bale of clean industrial stretch film and a bale of muddy agricultural film can differ by a wide margin in what the same machine will accept. The product page is explicit that wet film capacity is confirmed in a material trial rather than fixed by the model number alone, so treat the table as the envelope and the trial as the number you build your business case on.

The 2% or lower outlet moisture in the last column refers to the line after thermal drying, not to the squeezing stage on its own. More on that split below.

Anti-Wrapping: The Detail That Decides Everything

Ask any operator who has run film what their worst downtime cause is, and the answer is almost never a worn blade. It is a wrap: film wound tight around a shaft, a roller or a rotor end, requiring the line to be stopped, guarded, opened and cut free. Prevention starts at the bale breaker and continues through every transfer point, which is why the feed stage is a designed machine and not a conveyor belt.

Two practical rules follow from this for anyone specifying a film plant. First, throughput is set by the feed stage, not by the washer — if the metering device cannot present film at a steady rate, a larger wash unit buys nothing. Second, every downstream transfer should be as short and as positively driven as possible; gravity chutes and long free spans are where tangles form.

The Three Machines That Decide Output Quality

Once the film is reduced and washed, output quality is set by three machines. Each has published data you can compare directly.

1. Friction washing. High-speed friction between the rotor and the plastic strips soil, oil and printing ink residue from the surface, and spray bars carry it away. The FW series is published from FW-500 at 15 kW and 500 rpm with a 300-500 kg/h capacity and 2-4 m³/h water use, up to FW-1200 at 55 kW and 800 rpm with 1,500-2,000 kg/h and 8-12 m³/h. Rotation speed is adjustable by frequency converter. Material should be pre-reduced to roughly 10-30 mm: coarser than that and cleaning drops off, finer and the separation stages downstream become difficult. Heavily contaminated lines use two or three washers in series rather than one oversized unit.

2. Dewatering. This is where film departs from rigid practice. Vertical centrifugal machines are rated by dewatering rate — the VD series is published at 95% or higher — but they are built for flakes that can be thrown outward. Film needs the horizontal screw-press structure: the HD series is published at 3-15% outlet moisture depending on model, with HD-300 at 15 kW and a Ø300 mm screw handling 300-500 kg/h, HD-500 at 30 kW and Ø500 mm at 500-1,000 kg/h, and HD-800 at 45 kW and Ø800 mm at 1,000-2,000 kg/h. Note the published behaviour: on the same model, outlet moisture rises with throughput. See the dewatering machine page for both structures side by side.

3. Air separation. Light contamination that survives washing — paper fragments, fines, residual light film — is pulled out of the stream by air. The WX horizontal air separator is published at 92% or higher separation efficiency across WX-600, WX-800 and WX-1000, with capacities from 800-1,500 kg/h up to 2,500-3,000 kg/h and a 5-80 mm working particle range. Its one hard constraint is moisture: above roughly 10%, particles stick and efficiency falls. That is why air separation belongs after squeezing and drying, never straight out of the wash bath.

Water, Power and the Real Cost of Wet Throughput

The published line data puts water use at 3-5 t/h on the WL-500 rising to 12-20 t/h on the WL-5000, and total connected power at 80-120 kW rising to 250-300 kW. Both scale roughly with throughput, and both are stated for the line rather than a single machine — friction washers alone account for 2-4 m³/h at FW-500 up to 8-12 m³/h at FW-1200.

Two cost levers matter more than the headline numbers. The first is mechanical versus thermal dewatering: every point of water removed by a screw press is water the dryer does not have to evaporate, and drying is the most energy-intensive step in any wash line. The second is whether the plant runs a closed water circuit with treatment, in which case only make-up and evaporation losses are consumed, or discharges once-through. When you compare quotations from different suppliers, confirm which basis the water figure assumes before comparing the totals.

What Decides the Value of Your Film Flake

Buyers of washed film — whether they densify, agglomerate or granulate — grade on a short list, and each item maps back to a stage in the line:

• Soil and sand content — set by pre-wash intensity and the number of friction washers in series.
• Printing ink and label residue — lifted by friction washing with spray rinse; heavily inked material may need heated wash liquor.
• Residual moisture — set by the squeezing stage and the dryer; published line figure is 2% or lower after drying.
• Colour consistency — a sorting question rather than a washing one; the wash line's job is to deliver clean, uniform-density material to whatever sorting stage follows.

This is also why film lines and rigid lines are usually planned as separate plants rather than one line with a changeover. The PP/PE rigid plastic washing line and the PET bottle washing line both start from a crushing stage and rely on density separation; a film line starts from de-tangling and relies on squeezing. Trying to serve both from one set of machines usually means serving neither well.

Frequently Asked Questions